1. Technical Field of the Invention
The present invention relates to the formulation of novel cosmetic/dermatological compositions for topical application, for the photoprotection of the skin and/or the hair against ultraviolet radiation, in particular solar radiation, these novel compositions (hereinafter sometimes referred to simply as "sunscreen" or "antisun" compositions) having an improved SPF and an improved resistance to removal by water.
2. Description of the Prior Art
It is known to this art that light radiation of wavelengths of from 280 nm to 400 nm promotes tanning of the human epidermis, and that irradiation of wavelengths of from 280 nm to 320 nm, i.e., UV-B irradiation, causes skin burns and erythema which may be harmful to the development of a natural tan; hence, this UV-B radiation should be screened from the skin.
It is also known to this art that UV-A radiation, of wavelengths of from 320 nm to 400 nm, which causes tanning of the skin, also adversely affects it, especially in the case of sensitive skin or of skin which is continually exposed to solar radiation. UV-A rays cause, in particular, a loss of elasticity of the skin and the appearance of wrinkles, promoting premature skin aging. Such irradiation promotes triggering of the erythemal reaction or enhances this reaction in certain individuals and may even be the cause of phototoxic or photoallergic reactions. It is thus desirable to also screen out UV-A radiation.
A wide variety of cosmetic and/or dermatological compositions intended for the photoprotection (UV-A and/or UV-B) of the skin are known to this art.
These antisun compositions are quite often formulated as an emulsion of oil-in-water type (namely, a cosmetically and/or dermatologically acceptable vehicle, carrier or diluent comprising a continuous aqueous dispersing phase and a discontinuous oily dispersed phase) or of water-in-oil type (aqueous dispersed phase in a continuous oily phase) which contains, in various concentrations, one or more conventional lipophilic and/or hydrophilic organic photoscreening agents which are capable of selectively absorbing harmful or deleterious UV radiation. These screening agents (and the amounts thereof) are selected as a function of the desired sun protection factor (the sun protection factor (SPF) being expressed mathematically by the ratio of the irradiation time required to attain the erythema-forming threshold with the UV screening agent to the time required to attain the erythema-forming threshold in the absence of UV screening agent). In such emulsions, the hydrophilic screening agents are present in the aqueous phase and the lipophilic screening agents are present in the fatty phase.
Oil-in-water emulsions are generally more appreciated by consumers than water-in-oil emulsions, in particular on account of their pleasant feel (similar to water) and their presentation in the form of a non-greasy cream or milk. However, they also more readily lose their anti-UV protective efficacy as soon as they come into contact with water. The reason for this is that hydrophilic screening agents, in particular acidic such species, disappear in water, as a result of swimming in seawater or in a swimming pool, under the shower or while engaged in nautical sports. Thus, the antisun compositions comprising same, alone or combined with other lipophilic screening agents, no longer provide the desired initial protection once the substrate (skin or hair) on which they have been applied is contacted with water, this loss of protection factor by removal of the hydrophilic screening agent with water being all the more pronounced since the lipophilic/hydrophilic screening combination present in the composition is synergistic at the sun protection factor level.
Sunscreen compositions having improved SPFs and improved water-resistance may be provided as water-in-oil emulsions. This because a hydrophilic screening agent is more resistant to water in a water-in-oil emulsion than in an oil-in-water emulsion. However, as indicated above, such compositions are still not entirely satisfactory, insofar as after they have been applied, the user still experiences a particularly unpleasant sensation of greasiness.
It is also known to this art to improve the SPF of antisun/sunscreen emulsions, in particular oil-in-water emulsions, containing one or more hydrophilic screening agents by combining these sunscreens with certain very specific lipophilic screening agents, as described, for example, in EP-A-0,685,228, assigned to the assignee hereof. However, according to that technique, the improvements in the SPF obtained are based on the synergistic combination of specific hydrophilic and lipophilic screening agents (such as benzene-1,4-di(3-methylidene-10-camphorsulfonic) acid and 2-ethylhexyl .alpha.-cyano-.beta.,.beta.-diphenylacrylate in the case of EP-A-0,685,228) in standard oil-in-water emulsions, such that these improvements cannot be obtained generally, namely, irrespective of the hydrophilic and lipophilic screening agent(s) employed.
Thus, need continues to exist in this art for antisun/sunscreen compositions comprising both at least one hydrophilic screening agent and at least one lipophilic screening agent, and whose SPF is high and stable over time, irrespective of the hydrophilic and/or lipophilic screening agent(s) employed.